cpp: Minor optimization in remark lookup
cpp: Minor optimization in remark lookup

* lang/cpp/src/key.cpp (UserID::remark): Use C-API.

--
The other parts of that function already use the C API
so we can also avoid function calls for the keyListMode.

gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme,gpg/gpgme